1. Field of the Invention
The present invention relates to a charge/discharge system, and more particularly to a charge/discharge system for a battery of an electric vehicle.
2. Description of the Background Art
In recent years, the development of a next-generation power network called “Smart Grid” has attracted attention. One purpose of the Smart Grid is to optimize the supply and demand of power, and as shown in Japanese Patent Application Laid Open Gazette No. 2012-85383, it is proposed that a battery of an electric vehicle should be used as a buffer for reducing the peak of household electric power demand.
By charging the battery of the electric vehicle during a time period of low electric power demand and discharging the battery of the electric vehicle at the peak of electric power demand, for example, it is possible to reduce the peak of electric power demand. Further, since the electric power cost is generally low during the time period of low electric power demand, when the electric power charged during the time period is used during a time period where the electric power cost is high, it is possible to reduce household electricity rates. Furthermore, in emergency situations such as power outages or the like, by discharging the battery of the electric vehicle, it can be used as a power supply in such emergency situations.
Japanese Patent Application Laid Open Gazette Nos. 2012-85432 and 2011-182518 disclose exemplary constitutions of conventional electric vehicles. In each of these electric vehicles, to a high voltage wiring system, connected are a vehicle driving battery, a high-voltage equipment (a drive motor control device or a car charger), a high voltage relay, and the like. This is configured to supply power to all equipments relevant to the high voltage wiring system when a charge/discharge gun is connected to the vehicle.
The electric vehicles include an electric car which gains power by driving a motor using electric power charged in a secondary battery (storage battery) (hereinafter, referred to simply as “battery”) as a driving source, a plug-in hybrid electric vehicle (PHEV) which uses both an engine and a motor, and the like.
In the above-discussed conventional electric vehicles, since it is not assumed that the electric vehicle is connected to the smart grid and charge/discharge is performed for a long time and it is configured to turn on the power supplies of all the equipments relevant to a high voltage wiring system when a charge/discharge gun is connected to the vehicle, even the power supplies of the equipments irrelevant to charge/discharge, such as a drive motor control device or the like, are kept in an ON state for a long time when the electric vehicle is connected to the smart grid. This arises problems of wasting the electric power and accelerating degradation of parts.